Turning backward to gaze upon science's investigation into the human mind over the past two centuries, it's hard not to see phrenology, one of the great failures of science. Phrenology is the study of the shape of the skull, as well as bumps and depressions in the scalp. Phrenologists claimed that by analyzing these telltale signs, a person's intelligence, breeding and morality could be distinguished. Although it enjoyed international acclaim, phrenology was eventually -- and totally -- discredited.

Some wonder if the use of MRIs for mind reading is the new frontier of this old, discredited science. Phrenology was used to devalue entire groups of people, as some fear MRI mind mapping may be as well.

There are seemingly limitless ways that the MRI could be used to benefit mankind. MRIs could end up as a way to effectively read a person's thoughts before he even speaks them. The technology could allow law enforcement to see whether someone is lying or telling the truth. MRIs could thwart the next terrorist plot, or catch the next Green River Killer (this serial killer subverted a polygraph test and was let go).

Practically applied, an MRI could scan passengers at airports before they boarded a plane. Anyone displaying thoughts associated with hijacking or mass murder could be stopped before they committed such an act. Spies could be rooted out from clandestine service, and sexual predators could be identified before they ever claimed a first victim.

But many of the scientists conducted research say that this field is far too young to be currently used for any of these applications. The results are still too hazy. For one, although neurologists have identified certain parts of the brain which they associated with certain decisions, they're still unsure as to exactly why these processes take place. It's sort of like looking at a dark cloud and watching rain begin to fall from it, without any understanding of the process which creates the rain.

There are other, more easily conquered problems with using MRI as a window into the mind. MRIs are huge, hulking machines, which makes them difficult to transport. And for an MRI scan to be successful, the subject must lie perfectly still until the scan is completed. Even a movement as subtle as an eyebrow twitch can produce a useless scan.

But even if the technology does advance so MRIs are portable and can accurately scan a moving (and possibly unaware) person, should we use them for this application?

That's what's being posed by the Center for Cognitive Liberty and Ethics, a think tank that ponders the right of privacy for the thoughts of individuals. The problem with reading a person's thoughts, says the CCLE, is that technology like this could easily lead to scans of all of us to identify potential future criminals.

As justice in the Western world currently stands, people are convicted for crimes they're accused of committing rather than for crimes they may commit at some point in the future. Were MRIs used to scan minds to determine propensity towards crime, would this change? Could a future criminal find himself imprisoned or sequestered from society before he committed a crime?

Ultimately, the question is which is more valuable to society, personal liberty or personal security? This question has real applications right now, but if mind reading technology continues to advance, a new question may emerge: Do we have a right to privacy for our thoughts?